High voltage phase measurements



Jan. 26, 1960 F. c. DOBLE 2,922,951

HIGH VOLTAGE PHASE MEASUREMENTS Original Filed April 9, 1956 m-41W I @4 2,922,951 HIGH VOLTAGE PHASE MEASUREMENTS Frank C Doble, Belmont, Mass, assignor to Doble Engineering Company, Belmont, Mass., a corporation of Massachusetts Continuation of application Serial No.

1956. [US application March 10, 720,324

577,115, April 9, 1958, Serial No.

6 Claims. (Cl. 324-83) a continuation of my copending application Serial No. 577,115, now abandoned, filed April 9, 1956.

To specify the operating condition of an alternating current system, it is often necessary to make measure ments of phase relations that exist in the system. Usually this does not present any special problem insofar as relatively low voltage systems are concerned since convennecessitates that they be large to dissipate the power as heat. Also a crucial defect of high voltage resistors from the standpoint of phase measurements is that they have appreciable leakage capacitance which is subject to change and which it is difiicult if not impossible to correct for accurately. Hence, ordinarily, it cannot be assumed that the phase of the low voltage from such a resistor is correct unless, of course, there is no need to specify the phase relations under consideration with any degree of accuracy. In high voltage electrical systems just the converse is true, so that usually high-voltage resistors are seldom if ever used to obtain phase information.

As an alternative, potential transformers having high voltage primary windings and secondary windings which are adapted to provide suitable 10w working voltages have been used. However, such potential transformers have an inherent phase shift which varies significantly as a function of load, temperature, and other environmental conditions so that the phase of the low voltage derived by this means, may difier from that of the high voltage by as much as a degree or more. Moreover, high voltage potential transformers are expensive and bulky. Heretofore, the result has been that no practical Way was available for making accurate phase measurements at various selected :locations, especially in power systems where a knowledge of phase relations is often important for measurements and for load dispatching operations.

- The present invention has as its object the provision of United States Patent a method and apparatus for determining phase relations in high voltage electrical systems with an accuracy in the order of minutes.

A still further object of the invention is to provide a method and apparatus of the above-mentioned character which does not necessarily require that the system under consideration be de-energized at any time.

The novel features of the invention together with further objects and advantages thereof will become more readily apparent from a preferred embodiment illustrated in the accompanying drawing and described in detail hereinafter.

In Fig. 1 there is shown a high voltage line 12, which by way of and ground is an impedance device 14 of known power factor or defect angle. Devices suitable for this purpose and transformers. alternate layers of as to form, serve to divide the insulating layers. sented by the high voltage equally among the several schematically, each section is repreparallel combination of a capacitor and a shown in the drawing,

although it ordinarily a capacitor designed for operation at 110,000

charging current of the capacitor. Should this path be accidentally broken, there may also be provided between the terminal 24 (or 24') and ground, a protective device or gap 25.to prevent the voltage from becoming danger frequency as the high voltage. In addition, the potential coil has one of its terminals connected to ground and the other of its terminals connected to a line 36. The source of: low voltage may conveniently comprise a local 110 volt service outlet supplied from the same generating system as the high voltage. ,To represent ,a source of this kind, which is almost always readily available at a power station installation, there is shown in the drawing a transformer 30 through which the potential coil of the wattmeter 26 is energized. That is to say, transformer 30 has its primary winding 34 connected between the high voltage line 12 and ground, and its secondary winding 28 connected to the potential coil through the phase shifter 32. Preferably one terminal of the secondary winding 28 is grounded, as shown. In the normal case, there will be more than ,onesuch step-down transformer to provide the low voltage service, but this is obviously immaterial as regards the principles of the invention. Accordingly, the transformer 30 should be taken to represent not necessarily a single transformer, but as many step-down transformers as are generally employed for this purpose.

In operation, the phase of the low voltage on line 36 is caused to agree with that of the high voltage on line 12 so that any desired phase information, which involves the high voltage line, may be obtained through the use of ordinary low voltage measuring techniques. According to the invention, this adjustment is accomplished simply and safely, with due regard to the hazards normally associated with a high voltage power line. Thus, phase shifter 32 is adjusted until the power loss indicated by the wattmeter 26 corresponds to the actual power loss in the capacitor 14. The actual power loss may be determined in advance in accordance with the well known formula W equals VI cos 6, where W is the power loss, V is the high voltage across the capacitor, I is the total current therein, and cos is the known power factor of the capacitor. Ordinarily the impedance of the capacitor as well as its power factor will be known, so that the magnitude of the high voltage may be established through a measure of the current in the capacitor. An ammeter (not shown) may be connected in place of the current coil of the wattmeter to measure the current. Conversely, the current may be established on the basis of the capacitor impedance and the magnitude of the high voltage across the capacitor, as indicated by regular station equipment.

Once the wattmeter reading has been appropriately adjusted by means of the phase shifter so that the reading corresponds to the actual loss in the capacitor, it follows that the voltage on line 36 will have precisely the same phase as the high voltage. Since the line 36 carries a relatively low reference voltage, which is effectively isolated from the high voltage system by the capacitor, the line 36 may be used at will anywhere on the system without the attendant insulation problem that, as a practical matter, rules out the direct use of the high voltage for phase measuring purposes. If there is any shift in the phase of the reference voltage with respect to that of the high voltage, due to load changes on the low voltage service for example, then the phase shifter may be readjusted to compensate for such shifts as required.

Although the inventi n has been described in connection with a single reference voltage derived from a single high voltage conductor, it is contemplated that a reference voltage be derived in like manner from each high voltage conductor under consideration. The various reference voltages may conventional means, such as a phase meter or synchroscope, to obtain whateverphase information is desired to be known about the system. In fact, it will be appreciated that other conventional phase sensitive devices than a wattmeter may optionally be employed in the apparatus of the invention to establish the phase of the reference voltage.

then be compared inphase by any In Fig. 3 there is illustrated an alternative arrangement for deriving a suitable low working voltage which is locked in at the same frequency as the high voltage. Specifically, the secondary of the transformer 30 is connected to a synchronous motor 41 driving an A.C. generator 4-2. The generator in turn provides the requisite low voltage whose phase is to be made to agree with that of a high voltage. An advantage of this arrangement is that the generator itself may be adapted to serve as a phase shifting device simply by the provision of means to physically rotate the stator with respect to the rotor. This is illustrated diagrammatically by the gearing; arrangement in the drawing including a gear wheel 43 on the stator and worm 44 disposed in driving relation to the gear wheel.

Various such modifications that are within the spirit and scope of the invention will no doubt occur to those skilled in the art, so that the invention should not be deemed to be limited to the details of what has been illustrated and described herein by way of example; but rather it should be deemed to be limited only by the scope of the appended claims.

What is claimed is: j V

1. Apparatus for establishing a low voltage in a given phase relation to an unknown high voltage, said apparatus comprising an impedance device of known defect angle connected to the high voltage to provide a point of relatively low potential a source of low voltage having the same frequency as the unknown high voltage, a phase sensitive device having a first input circuit coupled to the low voltage source and a second input circuit coupled between said point of low potential and ground to provide an indication of the phase difference between said low voltage and the current flowing through said impedance device, and means to shift the phase of said low voltage to cause the indicated phase difference to represent the combination of said given phase relation and said defect angle.

2. Apparatus for establishing a low voltage in phase with an unknown high voltage, said apparatus comprising an impedance device of known defect angle connected to the high voltage to provide a point of relatively low potential a source of low voltage having the same frequency as the unknown high voltage, a phase sensitive device having a first input circuit coupled to the low voltage source and a second input circuit coupled between said point of low potential and ground to provide an indication of the phase difference between said low voltage and the current flowing through said impedance device, and means to shift the phase of said low voltage to cause the indicated phase difference to represent said defect angle.

3. Apparatus for establishing a low voltage in phase with an unknown high voltage, said apparatus comprising an impedance device of known power loss connected to the high voltage to provide a point of relatively low potential a source of low voltage having the same frequency as the unknown high voltage, a wattmeter having a potential coil coupled to the low voltage source and a current coil coupled between said point of low potential and ground, and means to shift the phase of said low voltage to cause the power loss indicated by said wattmeter to represent the actual power loss in 'said impedance device.

4. Apparatus to provide a low voltage in phase with an unknown high voltage, said apparatus comprising an impedance device of known defect angle connected to the high voltage to provide a point of relatively low potential, a synchronous motor energized by a voltage derived from the high voltage, an alternating current generator in driven relation to said motor, a phase sensitive device having a first input circuit coupled'to said generator and a second input circuit coupled between said point of low potential and ground to provide an indication of the phase difference between the generator voltage and the current flowing through said impedance device, and means to shift the phase of the generator voltage to cause the indicated phase diiference to represent said defect angle.

5. Apparatus as claimed in claim 4 wherein said phase shifting means includes a mechanism to vary the angular relation between the rotor and stator of the generator.

6. Apparatus for use in combination with an impedance device of known defect angle connected to a high voltage line for establishing a low voltage in a given phase relation to the high voltage, said apparatus comprising a source of low voltage having the same frequency as the unknown high voltage, a phase sensitive device having a first input circuit coupled to the low voltage source and a second input circuit coupled between a point of relatively low potential on said impedance device and ground to provide an indication of the phase difference between said low voltage and the current flowing through said impedance device, and means to shift the phase of said low voltage to cause the indicated phase diiference to represent the combination of said given phase relation and said defect angle.

References Cited in the file of this patent UNITED STATES PATENTS 1,617,912 Kafka et a1. Feb. 15, 1927 1,688,790 Cook Oct. 23, 1928 1,728,835 Petch Sept. 17, 1929 1,894,338 Austin Jan. 17, 1933 1,994,279 Higgins Mar. 12, 1935 2,225,653 Monk Dec. 24, 1940 2,432,214 Sontheimer Dec. 9, ,1947 2,436,479 Luck Feb. 25, 1948 2,600,204 Carleton June 10, 1952 2,694,794 Blomqvist NOV. 16, 1954 2,749,516 Ragazzini June 5, 1956 2,756,414 Doremus July 24, 1956 2,771,581 Stolzenbach Nov. 20, 1956 FOREIGN PATENTS 526,491 France Oct. 8, 1921 OTHER REFERENCES Accurate Oscilloscope Phase Shift Measurements,

article in Electronic D 34-35.

esign, January 15, 1956, pages 

